diff --git a/Makefile b/Makefile
index 313b80d..e6b6ceb 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,7 @@ BINDIR=$(PREFIX)/bin
 
 all: diff
 
-diff:
+diff: cmd/diff/main.ha
 	$(HARE) build $(HAREFLAGS) -o $@ cmd/$@/
 
 clean:
diff --git a/cmd/diff/main.ha b/cmd/diff/main.ha
index 943c971..5d1dbcf 100644
--- a/cmd/diff/main.ha
+++ b/cmd/diff/main.ha
@@ -1,5 +1,79 @@
 use fmt;
+use io;
+use os;
+use strings;
+
+
+const DELIM = "\n";
+
 
 export fn main() void = {
-	fmt::println("Hello world!")!;
+    const path = os::args[1];
+    const fh = os::open(path)!;
+
+    const other_path = os::args[2];
+    const other_fh = os::open(other_path)!;
+
+    compare_files(fh, other_fh);
+};
+
+
+fn compare_files(lhh: io::handle, rhh: io::handle) uint = {
+    // get lines from left hand file provided
+    const lhh_contents = io::drain(lhh)!;
+    const lhh_contents = strings::fromutf8(lhh_contents)!;
+    const lhh_lines = strings::split(lhh_contents, DELIM)!;
+    const lhh_num_lines = len(lhh_lines);
+    // get lines from right hand file provided
+    const rhh_contents = io::drain(rhh)!;
+    const rhh_contents = strings::fromutf8(rhh_contents)!;
+    const rhh_lines = strings::split(rhh_contents, DELIM)!;
+    const rhh_num_lines = len(rhh_lines);
+    // iteration
+    let lhh_i = 0z;
+    let rhh_i = 0z;
+    let cmp_res = 0i;
+    let rhh_mis_buffer: []*str = [];
+    let lhh_mis_buffer: []*str = [];
+
+
+    for (let i = 0z; lhh_i < lhh_num_lines && rhh_i < rhh_num_lines; i += 1) {
+        for (let j = 0z;
+                rhh_i < rhh_num_lines && lhh_i < lhh_num_lines;
+                j += 1) {
+            cmp_res = strings::compare(rhh_lines[rhh_i], lhh_lines[lhh_i]);
+            if (cmp_res < 0) {
+                append(rhh_mis_buffer, &rhh_lines[rhh_i])!;
+                rhh_i += 1;
+            } else if (cmp_res > 0) {
+                append(lhh_mis_buffer, &lhh_lines[lhh_i])!;
+                lhh_i += 1;
+            } else {
+                break;
+            };
+        };
+        if (len(rhh_mis_buffer) > 0 && len(lhh_mis_buffer) > 0) {
+            for (let j = 0z; j < len(lhh_mis_buffer); j += 1) {
+                fmt::printfln("< {}", *lhh_mis_buffer[j])!;
+            };
+            fmt::println("---")!;
+            for (let j = 0z; j < len(rhh_mis_buffer); j += 1) {
+                fmt::printfln("> {}", *rhh_mis_buffer[j])!;
+            };
+            for (let j = 0z; j < len(rhh_mis_buffer); j += 1) {
+                delete(rhh_mis_buffer[j]);
+            };
+            for (let j = 0z; j < len(lhh_mis_buffer); j += 1) {
+                delete(lhh_mis_buffer[j]);
+            };
+        };
+
+        lhh_i += 1;
+        rhh_i += 1;
+    };
+
+    free(rhh_mis_buffer);
+    free(lhh_mis_buffer);
+
+    return 0;
 };
diff --git a/testing/files/double_hello.ha b/testing/files/double_hello.ha
new file mode 100644
index 0000000..668258c
--- /dev/null
+++ b/testing/files/double_hello.ha
@@ -0,0 +1,7 @@
+use fmt;
+
+export fn main() void = {
+    const hello_str = "Hello world!";
+    fmt::println(hello_str)!;
+    fmt::println("Hello world!")!;
+};
diff --git a/testing/files/err_test.ha b/testing/files/err_test.ha
new file mode 100644
index 0000000..61ef873
--- /dev/null
+++ b/testing/files/err_test.ha
@@ -0,0 +1,5 @@
+use fmt;
+
+export fn main() void = {
+    fmt::println("Hello world!");
+};
diff --git a/testing/files/inc.ha b/testing/files/inc.ha
new file mode 100644
index 0000000..7c34f42
--- /dev/null
+++ b/testing/files/inc.ha
@@ -0,0 +1,17 @@
+use fmt;
+use io;
+use os;
+
+
+export fn main() void = {
+    let num = 4;
+    inc(&num);
+    inc(&num);
+    fmt::printfln("num = {}", num)!;
+    inc(&num);
+    fmt::printfln("num = {}", num)!;
+};
+
+fn inc(num: *int) void = {
+    *num += 1;
+};
diff --git a/testing/files/inc_dec.ha b/testing/files/inc_dec.ha
new file mode 100644
index 0000000..6a7c5ae
--- /dev/null
+++ b/testing/files/inc_dec.ha
@@ -0,0 +1,21 @@
+use fmt;
+use io;
+use os;
+
+
+export fn main() void = {
+    let num = 4;
+    inc(&num);
+    inc(&num);
+    fmt::printfln("num = {}", num)!;
+    dec(&num);
+    fmt::printfln("num = {}", num)!;
+};
+
+fn dec(num: *int) void = {
+    *num -= 1;
+};
+
+fn inc(num: *int) void = {
+    *num += 1;
+};
diff --git a/testing/files/long_test.ha b/testing/files/long_test.ha
new file mode 100644
index 0000000..10b8779
--- /dev/null
+++ b/testing/files/long_test.ha
@@ -0,0 +1,6 @@
+use fmt;
+
+export fn main() void = {
+    const hello_str = "Hello world!";
+    fmt::println(hello_str)!;
+};
diff --git a/testing/files/other_test.ha b/testing/files/other_test.ha
new file mode 100644
index 0000000..cdc1f0a
--- /dev/null
+++ b/testing/files/other_test.ha
@@ -0,0 +1,5 @@
+use fmt;
+
+export fn main() void = {
+    fmt::println("Hello world!")!;
+};
diff --git a/testing/files/test.ha b/testing/files/test.ha
new file mode 100644
index 0000000..cdc1f0a
--- /dev/null
+++ b/testing/files/test.ha
@@ -0,0 +1,5 @@
+use fmt;
+
+export fn main() void = {
+    fmt::println("Hello world!")!;
+};